Dell Dimension 8100 will not boot "Memory failed to be sized or enabled." PLZ HELP!!!

Ok, I have read everything, I have tried I think everything. Well I was cleaning my PC and I disconected everything, when I conected everything I powered up the PC and nothing came on, I hear the fan funning the CD wanting to bood the hard drive boot but then it stops. I checked the Diagnostic Codes and the A-B stay yellow and C-D stay green, it says is a Memory failed to be sized or enabled, now i added 4 RAMs cause I thought it would be the module, but still I get the same error, when I took the RAM out and I heard peeps, it was the following: 5-2-2-1 Unsupported RIMM device count/technology, I am not sure what is going on, the monitor stays black and with a yellow light and I get nothing. I NEED SOME ASSITENCE Please HELP someone....

RDRAM needs to be installed in PAIRS of identical type, e.g. 2x64MB, 2x128MB etc.. Each pair must also be either ECC or non-ECC.
You can have an ECC pair and a non-ECC pair, together they will work as non-ECC.
Dell Dimension 8100 take RDRAM 800. Under ME max 512MB memory, under W2K and XP up to 2GB.